A cofferdam lowering and positioning device and its usage method

Abstract

This invention discloses a cofferdam lowering and positioning device and its usage method, relating to the field of cofferdam construction technology. The cofferdam lowering and positioning device includes an outer fixing ring for fitting around a steel casing, and further includes a positioning mechanism, a control mechanism, a drive mechanism, and a connecting mechanism. The positioning mechanism is disposed between the outer fixing ring and the steel casing for clamping the steel casing. The control mechanism is connected to the positioning mechanism and is used to control the positioning mechanism to clamp or release the steel casing. The drive mechanism provides power to the control mechanism. The connecting mechanism connects the cofferdam and the outer fixing ring. This invention reduces the difficulty of lowering the cofferdam and achieves precise cofferdam positioning.

Description

Technical Field

[0001] This invention relates to the field of cofferdam construction technology, specifically a cofferdam lowering and positioning device and its usage method. Background Technology

[0002] Bridge foundation construction in water typically requires cofferdams as water-retaining structures to provide a waterless working environment. Steel cofferdams, such as single-wall and double-wall steel cofferdams, are the most commonly used form in deep-water bridge foundation construction. Steel cofferdams are generally prefabricated in sections in a factory and then transported to the site for section assembly and lowering. The section assembly and lowering are the most critical steps, requiring the positioning and sinking of the cofferdam sections in the water.

[0003] Currently, the positioning and lowering of steel cofferdams in water is achieved by welding simple arc-shaped plates onto the wall panels. These arc-shaped plates are then tightly fitted to the steel casing to guide the cofferdam's sinking. However, this existing technology has the following drawbacks: 1. Low positioning accuracy of the arc-shaped plates: After the cofferdam is lowered into the water, it is difficult to tightly fit the arc-shaped plates to the steel casing, requiring significant time for alignment and resulting in a lengthy operation. 2. In turbulent water, the cofferdam may move up and down due to the current, affecting the connection and welding of the upper and lower cofferdam segments. Existing positioning and lowering devices cannot temporarily fix the cofferdam. 3. Under the impact of the water flow, the positioning and lowering device may collide with the positioning steel casing. Without buffering, the positioning steel casing may be damaged under high-velocity water flow. 4. Direct contact between the arc-shaped plates and the steel casing results in high friction. During the sinking process, the cofferdam exerts a large axial force on the steel casing, potentially leading to localized instability. 5. Existing positioning and lowering devices are difficult to recover and reuse.

[0004] The patent document "A Precise Sinking and Limiting Device and Method for Double-Wall Steel Cofferdams in Deep-Water and Rapid-Flowing Rivers" (patent application number: CN202110780316.7) discloses a precise sinking and limiting device and method for double-wall steel cofferdams in deep-water and rapid-flowing rivers. Although it solves the above-mentioned problems to a certain extent, there are still some problems in actual use. The first support plate is always in close contact with the surface of the steel cofferdam during the lowering process, and the spring setting makes the arc formed by all the first support plates smaller than the cross-section of the steel casing in its natural state. Therefore, it is difficult to pass the steel casing through the gaps between the first support plates when lowering the cofferdam, making the installation very difficult, and it is also impossible to temporarily position the cofferdam. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a cofferdam lowering and positioning device and its usage method, which reduces the difficulty of lowering the cofferdam and achieves precise positioning of the cofferdam.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a cofferdam lowering and positioning device, comprising an outer fixing ring for being fitted onto the outside of a steel casing, and further comprising a positioning mechanism, a control mechanism, a drive mechanism, and a connecting mechanism; the positioning mechanism is disposed between the outer fixing ring and the steel casing for clamping the steel casing; the control mechanism is connected to the positioning mechanism for controlling the positioning mechanism to clamp or release the steel casing; the drive mechanism is used to provide power to the control mechanism; and the connecting mechanism is used to connect the cofferdam and the outer fixing ring.

[0007] Based on the above technical solution, the positioning mechanism includes several arc-shaped clamping blocks arranged in a ring.

[0008] Based on the above technical solution, a connecting rod is slidably connected through the arc-shaped clamping block. A buffer block is fixedly connected to one end of the connecting rod facing the steel casing, and a limit block is fixedly connected to the other end of the connecting rod. The arc-shaped clamping block has a storage groove for storing the buffer block, and the buffer block is fixedly connected to one end of a spring sleeved on the connecting rod, and the other end of the spring is fixedly connected to the inner wall of the storage groove.

[0009] Based on the above technical solution, multiple uniformly distributed steel balls are embedded and rolled on the side wall of the buffer block facing the steel casing.

[0010] Based on the above technical solution, the control mechanism includes a gear disk, several racks, and several synchronous gears; the gear disk is rotatably connected to the bottom surface of the outer fixed ring; the racks are arranged radially along the outer fixed ring, and the end of the rack facing the inner side of the outer fixed ring is connected to the arc-shaped clamping block in a one-to-one correspondence; the synchronous gears correspond to the racks in a one-to-one correspondence, and the synchronous gears mesh with the gear disk and the corresponding rack respectively.

[0011] Based on the above technical solution, the top surface of the outer fixed ring is provided with a guide block for mounting the rack and a gear frame for mounting the synchronous gear.

[0012] Based on the above technical solution, the drive mechanism includes a hydraulic rod, which is connected to one of the racks.

[0013] Based on the above technical solution, the driving mechanism further includes a connecting block, which has an installation groove for installing a hydraulic rod, and the connecting block is fixedly connected to the corresponding guide block.

[0014] Based on the above technical solution, the connecting mechanism includes a cofferdam fixing block fixedly connected to the outer wall of the cofferdam and a connecting fixing block fixedly connected to the end of the connecting block; a motor is fixedly connected to the middle of the side of the connecting fixing block facing the cofferdam fixing block, a screw is fixedly connected to the output shaft of the motor, a threaded cylinder is fixedly connected to the cofferdam fixing block at the position corresponding to the screw, and the threaded cylinder is threadedly connected to the screw; a guide rod is fixedly connected to the cofferdam fixing block symmetrically arranged with respect to the threaded cylinder, the guide rod passes through the connecting fixing block and is slidably connected to the connecting fixing block.

[0015] The present invention also provides a method of using the above-mentioned cofferdam lowering and positioning device, comprising the following steps:

[0016] Step S1. Drive the steel casing into the predetermined position on the riverbed bottom;

[0017] Step S2. Install the lowering positioning device at the designed position on the outer wall of the first cofferdam segment. Pull the rack with a hydraulic rod to make the arc-shaped clamp of the lowering positioning device open to the maximum extent.

[0018] Step S3. Position and lower the cofferdam segments so that each positioning device is fitted onto the corresponding steel casing, and then let the cofferdam segments float on the water surface.

[0019] Step S4. After the cofferdam floats to the designated position, extend the hydraulic rod to push the rack, thereby clamping it onto the outer wall of the steel casing through the arc-shaped clamping block, thus achieving the positioning and temporary fixation of the cofferdam; then, the second section of the cofferdam is connected and welded to the first section of the cofferdam.

[0020] Step S5. Control the hydraulic rod to shorten, so that the steel ball contacts the steel casing, allowing the first and second sections of the cofferdam to gradually sink under their own weight. After sinking to a self-floating state, the arc-shaped clamp is clamped onto the outer wall of the steel casing again to achieve temporary positioning of the cofferdam.

[0021] Step S6. Repeat steps S4 and S5 to assemble the cofferdam segments into a whole. Then, control the arc-shaped clamps to achieve precise positioning of the cofferdam as a whole. By filling the compartment with water and concrete, the cofferdam is lowered to the design position along the steel casing through the lowering positioning device.

[0022] Step S7. After the cofferdam is lowered into place, start the motor to make the screw rotate until it pushes the guide rod and the connecting fixing block to separate. Then, use a steel wire rope to hoist and retrieve the lowered positioning device.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. This invention, through the structural design of the positioning mechanism, allows the arc-shaped clamping block to slide to its maximum extent before lowering the cofferdam, facilitating the fitting of the positioning mechanism and the cofferdam into all the steel casings, reducing the difficulty of lowering the cofferdam and achieving precise positioning. Simultaneously, the steel ball design of the arc-shaped clamping block reduces the frictional force on the steel casings during the cofferdam's sinking process.

[0025] 2. During the lowering of the cofferdam, the cofferdam is easily impacted by the water flow, which causes the cofferdam to sway within a certain range. This invention can effectively avoid rigid collisions between the steel casing and the arc-shaped clamp during the swaying of the cofferdam, realize the buffer function between the positioning mechanism and the steel casing, and prevent damage to the steel casing from the impact of large water flows.

[0026] 3. The connection mechanism of the present invention is equipped with a motor-driven device. The positioning mechanism can be disassembled from the cofferdam simply by starting the motor. The positioning device can be easily lifted from the bottom by wire rope hoisting. There is no need for underwater construction by divers. The device is easy to disassemble and install and can be reused.

[0027] 4. Through the design of the positioning mechanism, when the cofferdam segment is lowered to the designated position, it can temporarily fix the cofferdam segment, thereby facilitating the connection between the upper and lower cofferdam segments, reducing the difficulty of cofferdam assembly and welding, and solving the problem that when the water flow is rapid, the cofferdam is affected by the water flow and moves up and down, making it impossible to connect and weld the cofferdam segments. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the cofferdam lowering and positioning device in an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the structure of the cofferdam lowering and positioning device after the connecting mechanism has been removed in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the arc-shaped clamping block in an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the connecting mechanism in an embodiment of the present invention;

[0032] Figure 5 This is a diagram showing the working state of the cofferdam lowering and positioning device in an embodiment of the present invention.

[0033] Figure label:

[0034] 1-Outer fixing ring;

[0035] 2-Positioning mechanism; 21-Arc-shaped clamping block; 22-Connecting rod; 23-Buffer block; 24-Limiting block; 25-Storage slot; 26-Spring; 27-Steel ball;

[0036] 3-Control mechanism; 31-Gear disc; 32-Rack; 33-Synchronizing gear; 34-Guide block; 35-Gear carrier;

[0037] 4-Drive mechanism; 41-Connecting block; 42-Mounting slot; 43-Hydraulic rod;

[0038] 5-Connecting mechanism; 51-Cofferdam fixing block; 52-Connecting fixing block; 53-Motor; 54-Screw; 55-Threaded cylinder; 56-Guide rod. Detailed Implementation

[0039] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0040] In the description of this invention, it should be noted that the directional terms such as "center", "lateral (X)", "longitudinal (Y)", "vertical (Z)", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this invention.

[0041] The following description, in conjunction with the accompanying drawings, further illustrates specific embodiments of the present invention, making the technical solution and its beneficial effects clearer and more explicit. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the invention.

[0042] See Figure 1 As shown, this embodiment of the invention provides a cofferdam lowering and positioning device, including an outer fixing ring 1 for being fitted onto the outside of a steel casing, and also including a positioning mechanism 2, a control mechanism 3, a drive mechanism 4, and a connecting mechanism 5; the positioning mechanism 2 is disposed between the outer fixing ring 1 and the steel casing, and is used to clamp the steel casing; the control mechanism 3 is connected to the positioning mechanism 2, and is used to control the positioning mechanism 2 to clamp or loosen the steel casing; the drive mechanism 4 is used to provide power to the control mechanism 3; the connecting mechanism 5 is used to connect the cofferdam and the outer fixing ring 1.

[0043] See Figure 2 and Figure 3As shown, the positioning mechanism 2 includes several arc-shaped clamping blocks 21 arranged in a ring. Specifically, a connecting rod 22 is slidably connected through and to the arc-shaped clamping block 21. A buffer block 23 is fixedly connected to one end of the connecting rod 22 facing the steel casing, and a limit block 24 is fixedly connected to the other end of the connecting rod 22. The arc-shaped clamping block 21 has a receiving groove 25 for receiving the buffer block 23, and one end of the buffer block 23 is fixedly connected to a spring 26 sleeved on the connecting rod 22, while the other end of the spring 26 is fixedly connected to the inner wall of the receiving groove 25. During the lowering of the cofferdam, the cofferdam is easily impacted by the water flow, causing it to sway within a certain range. The design of the spring 26 effectively avoids rigid collisions between the steel casing and the arc-shaped clamping blocks 21 during the swaying of the cofferdam, thus realizing the buffering function between the positioning mechanism 2 and the steel casing. Multiple evenly distributed steel balls 27 are embedded and rolled on the side wall of the buffer block 23 facing the steel casing. The design of the steel ball 27 ensures the smooth lowering of the cofferdam when the buffer block 23 presses against the outer wall of the steel casing, reducing friction on the steel casing during the lowering process. When the arc-shaped clamp 21 holds the steel casing, the buffer block 23 is completely retracted into the receiving groove 25, ensuring the clamping and fixing effect of the arc-shaped clamp 21 on the steel casing. It should be noted that the positioning mechanism 2 provides temporary fixation when the cofferdam is lowered to the designated position, facilitating the installation and fixing of the upper and lower cofferdam segments. Furthermore, the arc-shaped clamp 21 enables precise positioning of the cofferdam, making installation easier and reducing the difficulty of cofferdam installation.

[0044] See Figure 2 As shown, the control mechanism 3 includes a gear disk 31, several racks 32, and several synchronous gears 33. The gear disk 31 is rotatably connected to the bottom surface of the outer fixed ring 1. The racks 32 are arranged radially along the outer fixed ring 1, and one end of the rack 32 facing inward of the outer fixed ring 1 is connected to the arc-shaped clamping block 21. The synchronous gears 33 correspond one-to-one with the racks 32, and the synchronous gears 33 mesh with the gear disk 31 and the corresponding racks 32 respectively. Specifically, the top surface of the outer fixed ring 1 is provided with a guide block 34 for mounting the racks 32 and a gear carrier 35 for mounting the synchronous gears 33. Furthermore, the guide block 32 and the gear carrier 34 are arranged alternately. When one of the racks 32 slides along the guide block 34, it drives the corresponding synchronous gear 33 to rotate. The synchronous gear 33 drives the gear disc 31 to rotate, thereby driving all the synchronous gears 33 to rotate. Finally, all the racks 32 slide synchronously and drive the arc-shaped clamping block 21 to clamp and fix it on the outer wall of the steel casing. Since the position of the arc-shaped clamping block 21 is adjustable, when lowering the cofferdam, the arc-shaped clamping block 21 is first slid to its maximum extent to facilitate the placement of the positioning mechanism 2 and the cofferdam into all the steel casings, reducing the difficulty of lowering the cofferdam. After the cofferdam is lowered to the designated position, the positioning mechanism 2 and the cofferdam are fixed on the steel casing by the arc-shaped clamping block 21.

[0045] See Figure 2 As shown, the drive mechanism 4 includes a hydraulic rod 43, which is connected to one of the racks 32. Specifically, the drive mechanism 4 also includes a connecting block 41, which has a mounting groove 42 for mounting the hydraulic rod 43, and the connecting block 41 is fixedly connected to the corresponding guide block 34. It should be noted that the hydraulic rod 43 provides the driving force, thereby driving one of the racks 32 to slide along the guide block 34, realizing the clamping and fixing of the arc-shaped clamping block 21 on the steel casing.

[0046] See Figure 4 As shown, the connecting mechanism 5 includes a cofferdam fixing block 51 fixedly connected to the outer wall of the cofferdam and a connecting fixing block 52 fixedly connected to the end of the connecting block 41; a motor 53 is fixedly connected to the middle of the side of the connecting fixing block 52 facing the cofferdam fixing block 51, and a screw 54 is fixedly connected to the output shaft of the motor 53; a threaded cylinder 55 is fixedly connected to the cofferdam fixing block 51 at the position corresponding to the screw 54, and the threaded cylinder 55 is threadedly connected to the screw 54; a guide rod 56 is fixedly connected to the cofferdam fixing block 51 symmetrically arranged with respect to the threaded cylinder 55, and the guide rod 56 passes through the connecting fixing block 52 and is slidably connected to the connecting fixing block 52.

[0047] Through the above design, the positioning mechanism 2 is fixed to the outer wall of the cofferdam using the threaded cylinder 55 and the screw 54. When it is necessary to remove the positioning mechanism 2 from the cofferdam, it is only necessary to start the motor 53 to make the screw 54 rotate until it pushes the guide rod 56 and the connecting fixing block 52 to separate. At the same time, the screw 54 and the threaded cylinder 55 separate, and the positioning mechanism 2 can be removed from the cofferdam. When retrieving the positioning mechanism 2, a steel wire rope is tied to the guide block 34, and the positioning mechanism 2 can be pulled up from the water directly through the steel wire rope. When retrieving the positioning mechanism 2, there is no need for workers to dive, which improves the safety of the workers.

[0048] See Figure 5 As shown, this embodiment of the invention provides a method for using the above-mentioned cofferdam lowering and positioning device, including the following steps:

[0049] Step S1. Based on the design location of the cofferdam and the dimensions of the positioning device, mark the position of the positioning steel casing on the drilling platform or floating platform, and then use a crawler crane and vibratory hammer to drive the positioning steel casing into the riverbed.

[0050] Step S2. Inside the cofferdam processing plant, install a lowering positioning device at the designed position on the outer wall of the first cofferdam segment. Pull the rack with a hydraulic rod to make the arc-shaped clamp of the lowering positioning device open to the maximum extent.

[0051] Step S3. Transport the first cofferdam segment from the processing plant to the construction site by barge. The floating crane is anchored using the "four-cable positioning method" to lift the first cofferdam segment from the barge. By adjusting the four cables of the floating crane, the position of the floating crane is moved to position and lower the lifted cofferdam segment. Each lowering positioning device is fitted onto the steel casing. Then, the cofferdam segment is allowed to float on the water surface, and the floating crane and barge are withdrawn.

[0052] Step S4. After the cofferdam floats to the designated position, extend the hydraulic rod to push the rack, which clamps the cofferdam onto the outer wall of the steel casing via the arc-shaped clamps, thus achieving positioning and temporary fixation of the cofferdam. The second section of the cofferdam is transported to the construction site by barge and floating crane, and then docked and welded with the first section of the cofferdam.

[0053] Step S5. Control the hydraulic rod to shorten, so that the steel ball contacts the steel casing, allowing the first and second sections of the cofferdam to gradually sink under their own weight. After sinking to a self-floating state, clamp the arc-shaped clamp block on the outer wall of the steel casing again to achieve temporary positioning of the cofferdam.

[0054] Step S6. Repeat steps S4 and S5 to assemble the cofferdam segments into a whole. Then, control the arc-shaped clamps to achieve precise positioning of the entire cofferdam. By filling the compartments with water and concrete, the cofferdam is lowered to the design position along the steel casing through the lowering positioning device.

[0055] Step S7. After the cofferdam is lowered into place, start the motor to make the screw rotate until it pushes the guide rod and the connecting fixing block to separate. Then, use a steel wire rope to hoist and retrieve the lowered positioning device.

[0056] In the description of this specification, references to terms such as "an embodiment," "preferred," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. Illustrative expressions of the above terms in this specification do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0057] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A cofferdam lowering and positioning device, comprising an outer fixing ring (1) for being fitted onto the outside of a steel casing, characterized in that: It also includes a positioning mechanism (2), a control mechanism (3), a drive mechanism (4), and a connecting mechanism (5); The positioning mechanism (2) is set between the outer fixing ring (1) and the steel casing, and is used to clamp the steel casing; The control mechanism (3) is connected to the positioning mechanism (2) and is used to control the positioning mechanism (2) to clamp or release the steel casing; The drive mechanism (4) is used to provide power to the control mechanism (3); The connecting mechanism (5) is used to connect the cofferdam and the outer fixing ring (1).

2. The cofferdam lowering and positioning device as described in claim 1, characterized in that: The positioning mechanism (2) includes several arc-shaped clamps (21) arranged in a ring.

3. The cofferdam lowering and positioning device as described in claim 2, characterized in that: A connecting rod (22) is slidably connected through the arc-shaped clamping block (21). A buffer block (23) is fixedly connected to one end of the connecting rod (22) facing the steel casing, and a limit block (24) is fixedly connected to the other end of the connecting rod (22). The arc-shaped clamping block (21) has a storage groove (25) for storing the buffer block (23), and one end of the buffer block (23) is fixedly connected to a spring (26) sleeved on the connecting rod (22), and the other end of the spring (26) is fixedly connected to the inner wall of the storage groove (25).

4. The cofferdam lowering and positioning device as described in claim 3, characterized in that: The buffer block (23) has multiple uniformly distributed steel balls (27) embedded and rolled on the side wall facing the steel casing.

5. The cofferdam lowering and positioning device as described in claim 4, characterized in that: The control mechanism (3) includes a gear disk (31), several racks (32) and several synchronous gears (33); the gear disk (31) is rotatably connected to the bottom surface of the outer fixed ring (1); the racks (32) are arranged radially along the outer fixed ring (1), and one end of the rack (32) facing the inner side of the outer fixed ring (1) is connected to the arc-shaped clamp (21) in a one-to-one correspondence; the synchronous gears (33) correspond to the racks (32) in a one-to-one correspondence, and the synchronous gears (33) mesh with the gear disk (31) and the corresponding racks (32) respectively.

6. The cofferdam lowering and positioning device as described in claim 5, characterized in that: The top surface of the outer fixed ring (1) is provided with a guide block (34) for mounting the rack (32) and a gear carrier (35) for mounting the synchronous gear (33).

7. The cofferdam lowering and positioning device as described in claim 6, characterized in that: The drive mechanism (4) includes a hydraulic rod (43) connected to one of the racks (32).

8. The cofferdam lowering and positioning device as described in claim 7, characterized in that: The drive mechanism (4) also includes a connecting block (41), which has a mounting groove (42) for mounting a hydraulic rod (43), and the connecting block (41) is fixedly connected to the corresponding guide block (34).

9. The cofferdam lowering and positioning device as described in claim 8, characterized in that: The connecting mechanism (5) includes a cofferdam fixing block (51) fixedly connected to the outer wall of the cofferdam and a connecting fixing block (52) fixedly connected to the end of the connecting block (41); a motor (53) is fixedly connected to the middle of the side of the connecting fixing block (52) facing the cofferdam fixing block (51), a screw (54) is fixedly connected to the output shaft of the motor (53), a threaded cylinder (55) is fixedly connected to the cofferdam fixing block (51) at the position corresponding to the screw (54), and the threaded cylinder (55) is threadedly connected to the screw (54); a guide rod (56) is fixedly connected to the cofferdam fixing block (51) symmetrically arranged with respect to the threaded cylinder (55), the guide rod (56) passes through the connecting fixing block (52) and is slidably connected to the connecting fixing block (52).

10. A method of using the cofferdam lowering and positioning device according to claim 9, characterized in that, Includes the following steps: Step S1. Drive the steel casing into the predetermined position on the riverbed bottom; Step S2. Install the lowering positioning device at the designed position on the outer wall of the first cofferdam segment. Pull the rack (32) with the hydraulic rod (43) to make the arc-shaped clamp (21) of the lowering positioning device open to the maximum extent. Step S3. Position and lower the cofferdam segments so that each positioning device is fitted onto the corresponding steel casing, and then let the cofferdam segments float on the water surface. Step S4. After the cofferdam floats to the designated position, the hydraulic rod (43) is extended to push the rack (32), thereby clamping it to the outer wall of the steel casing through the arc-shaped clamp (21) to achieve the positioning and temporary fixation of the cofferdam; then the second section of the cofferdam is connected and welded to the first section of the cofferdam. Step S5. Control the hydraulic rod (43) to shorten, so that the steel ball (27) contacts the steel casing, allowing the first and second sections of the cofferdam to gradually sink under their own weight. After sinking to the self-floating state, the arc-shaped clamp (21) is clamped on the outer wall of the steel casing again to achieve temporary positioning of the cofferdam. Step S6. Repeat steps S4 and S5 to assemble each segment of the cofferdam into a whole. Then control the arc-shaped clamp (21) to achieve precise positioning of the whole cofferdam. By filling the compartment with water and concrete, the cofferdam sinks to the design position along the steel casing through the lowering positioning device. Step S7. After the cofferdam is lowered into place, start the motor (53) to make the screw (54) rotate until it pushes the guide rod (56) and the connecting fixing block (52) to separate. Then, use a steel wire rope to hoist and retrieve the lowered positioning device.

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